SYSTEMS FOR DRIVING DISPLAYS
A system is configured to drive a display device having a number of cholesteric liquid crystal (CHLC) pixels. The system comprises a processor configured to receive a first set of gray levels for a first image frame and a second set of gray levels for a second image frame, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame and the second set of gray levels is related to a second intensity state of each of the CHLC pixels in the second image frame, and a look-up table (LUT) configured to output a third set of gray levels based on the first set of gray levels and the second set of gray levels, wherein the third set of gray levels is related to an addressing voltage to be written to each of the CHLC pixels so as to change each of the CHLC pixels from the first intensity state to the second intensity state.
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The present invention relates to liquid crystal displays and, more particularly, to systems for driving displays having a cholesteric liquid crystal material.
Nowadays, liquid crystal displays may have taken the place of traditional displays because of low power consumption. Moreover, remarkable advance in liquid crystal material research has resulted in the discovery of bistable chiral nematic liquid crystal materials or cholesteric liquid crystal (CHLC) materials. Generally, CHLC may exhibit grey scale properties depend on a voltage value applied thereto. Moreover, CHLC materials may consume less power than other liquid crystal materials because the former may be able to remain a given state in absence of an electric field applied thereto. Accordingly, CHLC displays may advantageously provide relatively high luminance and contrast.
Many driving schemes have been proposed to drive a CHLC display. An example of the conventional driving schemes may include the steps of refreshing one of a number of “N” rows in a frame followed by addressing the one of the rows until all of the rows in the frame are refreshed and addressed. Accordingly, a frame time TFRAME required to drive the frame may be calculated below.
TFRAME=TRESET×N+TADDRESSING×N
Where TRESET is the time required to refresh each row and TADDRESSING is the time required to address the each row.
Another example of the conventional driving schemes may include the steps of refreshing all of the “N” rows at a time and then addressing each of the rows in the frame. Accordingly, the frame time TFRAME may be calculated below.
TFRAME=TRESET+TADDRESSING×N
The later driving scheme may be more efficient than the former one in view of the frame time required. However, with the increasing interest in display devices with faster response speeds and higher data rates, it may be desirable to have a driving scheme with a faster driving time than the conventional driving schemes.
BRIEF SUMMARY OF THE INVENTIONExamples of the present invention may provide a system for driving a display device having a number of cholesteric liquid crystal (CHLC) pixels. The system comprises a processor configured to receive a first set of gray levels for a first image frame and a second set of gray levels for a second image frame, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame and the second set of gray levels is related to a second intensity state of the each of the CHLC pixels in the second image frame, and a look-up table (LUT) configured to output a third set of gray levels based on the first set of gray levels and the second set of gray levels, wherein the third set of gray levels is related to an addressing voltage to be written to each of the CHLC pixels so as to change each of the CHLC pixels from the first intensity state to the second intensity state.
Some examples of the present invention may also provide a system for driving a display device having a number of cholesteric liquid crystal (CHLC) pixels. The system comprises a sensor configured to detect a first set of gray levels of the CHLC pixels for a first image frame displayed on the display device, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame, a processor configured to receive a second set of gray levels for a second image frame, wherein the second set of gray levels is related to a second intensity state of the each of the CHLC pixels in the second image frame, and a look-up table (LUT) configured to output a third set of gray levels based on the first set of gray levels from the sensor and the second set of gray levels from the processor, wherein the third set of gray levels is related to an addressing voltage to be written to each of the CHLC pixels so as to change each of the CHLC pixels from the first intensity state to the second intensity state.
Examples of the present invention may further provide a system for driving a display device having a number of cholesteric liquid crystal (CHLC) pixels. The system comprises a processor configured to receive a first set of gray levels for a first image frame and a second set of gray levels for a second image frame, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame and the second set of gray levels is related to a second intensity state of the each of the CHLC pixels in the second image frame, a sensor configured to detect a third set of gray levels of the CHLC pixels for the first image frame displayed on the display device, wherein the third set of gray levels is related to a third intensity state of each of the CHLC pixels displayed in the first image frame, a first look-up table (LUT) configured to output an index based on the first set of gray levels and the third set of gray levels, wherein the index is related to an environmental change, and a second LUT configured to output a fourth set of gray levels based on the second set of gray levels from the processor, the third set of gray levels from the sensor and the index from the first LUT, wherein the fourth set of gray levels is related to an addressing voltage to be written to each of the CHLC pixels so as to change each of the CHLC pixels from the third intensity state to the second intensity state.
Other objects, advantages and novel features of the present invention will be drawn from the following detailed examples of the present invention with attached drawings.
The foregoing summary as well as the following detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:
Reference will now be made in detail to the present examples of the invention illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements.
Firstly, a CHLC pixel may be refreshed to the initial P state or the initial F state. Taking the initial P state as an example, it may be identified that when a voltage of approximately 40 volts (V) is applied, a maximum reflectance level may be reached. A voltage of approximately 20V may be applied to the CHLC for duration of 30 milliseconds (ms), which is long enough to change the CHLC pixel from the initial P state to the initial F state. A voltage source providing the 40V voltage level may then be removed. Subsequently, a voltage of approximately 1V is applied, resulting in a first point RP1. Next, the refreshing step may be repeated by applying the 40V voltage level to the CHLC for 30 ms and then removing the voltage source. Subsequently, an addressing step may be repeated by applying a voltage of approximately 2V, resulting in a second point RP2. The refreshing step followed by an addressing step may be repeated by using the 40V voltage level as a refresh voltage and using voltages of 3V to 40V as an addressing voltage one at a time. Consequently, the curve 101 may be obtained.
In plotting the curve 101, it may be identified that when a voltage of approximately 22V is applied, a minimum reflectance level may be reached. The curve 104 may be obtained in a similar fashion by using a 22V voltage as a refresh voltage while using voltages of 1V to 40V as an addressing voltage one at a time.
Likewise, in plotting the curve 101, it may be identified that when a voltage of approximately 26.5V is applied, a 30% reflectance level may be reached. The curve 103 may be obtained in a similar fashion by using a 26.5V voltage as a refresh voltage while using voltages of 1V to 40V as an addressing voltage one at a time.
Likewise, in plotting the curve 101, it may be identified that when a voltage of approximately 28V is applied, an 80% reflectance level may be reached. The curve 102 may be obtained in a similar fashion by using a 28V voltage as a refresh voltage while using voltages of 1V to 40V as an addressing voltage one at a time. Skilled persons in the art will understand that other curves representing other reflectance levels may be obtained even though only four curves 101 to 104 are illustrated.
Generally, CHLC material may exhibit different reflectance levels when a given voltage is applied thereto. For example, in a first hysteresis region HR1, if a voltage of, for example, 27V, is applied, the CHLC pixel may exhibit four different reflectance levels corresponding to the curves 101 to 104, which is undesirable. Alternatively, if an 80% reflectance, for example, is to be written in a next frame for a CHLC pixel, four different voltage levels corresponding to the curves 101 to 104 may be possible, which is also undesirable. To identify an addressing voltage from the curves 101 to 104, voltage levels in one of the first hysteresis region HR1 ranging from approximately 25V to 30V and a second hysteresis region HR2 ranging from approximately 12V to 17V may be coded in gray level. Taking the first hysteresis region HR1 as an example, the voltages 25V, 26.5V, 28V and 30V in this region may be coded in a coding algorithm into “00,” “01,” “10” and “11,” respectively. The voltage gray levels may be stored in the LUT 12 illustrated in
Furthermore, the gray level GLN or GLN−1 of each pixel may correspond to one of the reflectance levels represented by the curves 101 to 104. For example, a gray level of the CHLC pixel ranging from 0 to 2 may correspond to the 5% reflectance curve 104, and a gray level ranging from 235 to 255 may correspond to the 100% reflectance curve 101.
Referring back to
The output voltage VM from the voltage modulator 14 may then be written to the CHLC pixel through a probe 15 so that the gray level of the CHLC pixel may be changed from the first state GLN−1 to the second state GLN.
TFRAME=TADDRESSING×N
Referring to
In describing representative examples of the present invention, the specification may have presented the method and/or process of operating the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.
It will be appreciated by those skilled in the art that changes could be made to the examples described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular examples disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
Claims
1. A system for driving a display device having a number of cholesteric liquid crystal (CHLC) pixels, the system comprising:
- a processor configured to receive a first set of gray levels for a first image frame and a second set of gray levels for a second image frame, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame and the second set of gray levels is related to a second intensity state of the each of the CHLC pixels in the second image frame; and
- a look-up table (LUT) configured to output a third set of gray levels based on the first set of gray levels and the second set of gray levels, wherein the third set of gray levels is related to an addressing voltage to be written to the each of the CHLC pixels so as to change the each of the CHLC pixels from the first intensity state to the second intensity state.
2. The system of claim 1, wherein each of the third set of gray levels is related to one of voltage levels in a hysteresis region of a set of reflectance-voltage (RV) curves.
3. The system of claim 2, wherein each of the first set of gray levels is related to one of the set of RV curves and each of the second set of gray levels is related to one of reflectance levels represented by one of the set of RV curves.
4. The system of claim 3, wherein the processor is configured to identify the addressing voltage based on an intersection point of the one of the set of RV curves and the one of reflectance levels.
5. The system of claim 1 further comprising a memory to store the first set of gray levels.
6. The system of claim 1 further comprising:
- a mapper configured to map each of the third set of gray levels into a voltage level.
7. The system of claim 6 further comprising:
- a modulator configured to convert a voltage level from the mapper into one of a uni-polar pulse voltage, a bipolar pulse voltage and a pulse width modulation (PWM) voltage.
8. A system for driving a display device having a number of cholesteric liquid crystal (CHLC) pixels, the system comprising:
- a sensor configured to detect a first set of gray levels of the CHLC pixels for a first image frame displayed on the display device, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame;
- a processor configured to receive a second set of gray levels for a second image frame, wherein the second set of gray levels is related to a second intensity state of the each of the CHLC pixels in the second image frame; and
- a look-up table (LUT) configured to output a third set of gray levels based on the first set of gray levels from the sensor and the second set of gray levels from the processor, wherein the third set of gray levels is related to an addressing voltage to be written to the each of the CHLC pixels so as to change the each of the CHLC pixels from the first intensity state to the second intensity state.
9. The system of claim 8, wherein each of the third set of gray levels is related to one of voltage levels in a hysteresis region of a set of reflectance-voltage (RV) curves.
10. The system of claim 9, wherein each of the first set of gray levels is related to one of the set of RV curves and each of the second set of gray levels is related to one of reflectance levels represented by one of the set of RV curves.
11. The system of claim 10, wherein the processor is configured to identify the addressing voltage based on an intersection point of the one of the set of RV curves and the one of reflectance levels.
12. The system of claim 8 further comprising:
- a mapper configured to map each of the third set of gray levels into a voltage level.
13. The system of claim 12 further comprising:
- a modulator configured to convert a voltage level from the mapper into one of a uni-polar pulse voltage, a bipolar pulse voltage and a pulse width modulation (PWM) voltage.
14. The system of claim 7 further comprising:
- a probe configured to write a set of addressing voltages to an M-th row of the CHLC pixels in an N-th image frame as the sensor detects a set of gray levels of an (M+1)-th row of the CHLC pixels in an (N−1)-th image frame, M, N being positive integers.
15. A system for driving a display device having a number of cholesteric liquid crystal (CHLC) pixels, the system comprising:
- a processor configured to receive a first set of gray levels for a first image frame and a second set of gray levels for a second image frame, wherein the first set of gray levels is related to a first intensity state of each of the CHLC pixels in the first image frame and the second set of gray levels is related to a second intensity state of the each of the CHLC pixels in the second image frame;
- a sensor configured to detect a third set of gray levels of the CHLC pixels for the first image frame displayed on the display device, wherein the third set of gray levels is related to a third intensity state of each of the CHLC pixels displayed in the first image frame;
- a first look-up table (LUT) configured to output an index based on the first set of gray levels and the third set of gray levels, wherein the index is related to an environmental change; and
- a second LUT configured to output a fourth set of gray levels based on the second set of gray levels from the processor, the third set of gray levels from the sensor and the index from the first LUT, wherein the fourth set of gray levels is related to an addressing voltage to be written to the each of the CHLC pixels so as to change the each of the CHLC pixels from the third intensity state to the second intensity state.
16. The system of claim 15, wherein each of the fourth set of gray levels is related to one of voltage levels in a hysteresis region of a set of reflectance-voltage (RV) curves.
17. The system of claim 16, wherein each of the first set of gray levels is related to one of the set of RV curves and each of the second set of gray levels is related to one of reflectance levels represented by one of the set of RV curves.
18. The system of claim 17, wherein the processor is configured to identify the addressing voltage based on an intersection point of the one of the set of RV curves and the one of reflectance levels.
19. The system of claim 15 further comprising a memory to store the first set of gray levels.
20. The system of claim 15 further comprising:
- a mapper configured to map each of the fourth set of gray levels into a voltage level.
21. The system of claim 20 further comprising:
- a modulator configured to convert a voltage level from the mapper into one of a uni-polar pulse voltage, a bipolar pulse voltage and a pulse width modulation (PWM) voltage.
22. The system of claim 15 further comprising:
- a probe configured to write a set of addressing voltages to an M-th row of the CHLC pixels in an N-th image frame as the sensor detects a set of gray levels of an (M+1)-th row of the CHLC pixels in an (N−1)-th image frame, M, N being positive integers.
Type: Application
Filed: Dec 18, 2008
Publication Date: Jun 24, 2010
Applicant: INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE (Chutung)
Inventors: Tai-Ann Chen (Sindian City), Chih-Jen Chen (Yongkang City), Chiao-Nan Huang (Sijhou Township), Chao-Ching Liang (Jhonghe City)
Application Number: 12/337,626